U.S. patent number 7,542,189 [Application Number 11/533,854] was granted by the patent office on 2009-06-02 for light scanning apparatus and image forming apparatus using the light scanning apparatus.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Hidekazu Shimomura, Tokuji Takizawa, Ken Tanimura.
United States Patent |
7,542,189 |
Tanimura , et al. |
June 2, 2009 |
Light scanning apparatus and image forming apparatus using the
light scanning apparatus
Abstract
A light scanning apparatus including a semiconductor laser which
emits a light beam having a wavelength equal to or less than 450
nm, an incidence optical system which makes the light beam, emitted
from the semiconductor laser, incident on a deflector for scanning
in deflection, an imaging optical system which images the light
beam scanned in deflection by the deflector to a surface to be
scanned, a light intensity detector which detects fluctuations in
spectral transmittances of the incidence optical system and of the
imaging optical system, which are caused as a concomitant of a
fluctuation in wavelength of the light beam which is emitted from
the semiconductor laser and passes through the incident optical
system and the imaging optical system, and an automatic power
controller which automatically controls a light emission output of
the semiconductor laser on the basis of a detection value detected
by the light intensity detector.
Inventors: |
Tanimura; Ken (Utsunomiya,
JP), Shimomura; Hidekazu (Yokohama, JP),
Takizawa; Tokuji (Utsunomiya, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
37910846 |
Appl.
No.: |
11/533,854 |
Filed: |
September 21, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070081213 A1 |
Apr 12, 2007 |
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Foreign Application Priority Data
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Sep 27, 2005 [JP] |
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2005-280432 |
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Current U.S.
Class: |
359/205.1 |
Current CPC
Class: |
G02B
26/127 (20130101) |
Current International
Class: |
G02B
26/08 (20060101) |
Field of
Search: |
;359/205-208,216
;250/339.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Cherry; Euncha P
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A light scanning apparatus comprising: a semiconductor laser
which emits a light beam having a wavelength equal to or less than
450 nm; an incidence optical system which makes the light beam,
emitted from said semiconductor laser, incident on a deflection
means for scanning in deflection; an imaging optical system which
images the light beam scanned in deflection by said deflection
means to a surface to be scanned; light intensity detection means
which detects fluctuations in spectral transmittances of said
incidence optical system and of said imaging optical system, which
are caused as a concomitant of a fluctuation in wavelength of the
light beam which is emitted from said semiconductor laser and
passes through said incident optical system and said imaging
optical system; and automatic power control means which
automatically controls a light emission output of said
semiconductor laser on the basis of a detection value detected by
said light intensity detection means.
2. A light scanning apparatus according to claim 1, wherein said
light intensity detection means is disposed in a position conjugate
to the scanned surface.
3. An image forming apparatus comprising: a light scanning
apparatus according to claim 1; a photosensitive body which is
disposed on the scanned surface; a developing unit which develops,
as a toner image, an electrostatic latent image formed on said
photosensitive body by light beams used for scanning by said light
scanning apparatus; a transfer unit which transfers the developed
toner image onto a transferred material; and a fixing unit which
fixes the transferred toner image onto the transferred
material.
4. An image forming apparatus according to claim 3, further
comprising a printer controller which converts code data inputted
from an external apparatus into an image signal and inputs the
image signal to said light scanning apparatus.
5. A light scanning apparatus according to claim 1, wherein said
imaging optical system includes a plastic lens.
6. An image forming apparatus comprising: a light scanning
apparatus according to claim 5; a photosensitive body which is
disposed on the scanned surface; a developing unit which develops,
as a toner image, an electrostatic latent image formed on said
photosensitive body by light beams used for scanning by said light
scanning apparatus; a transfer unit which transfers the developed
toner image onto a transferred material; and a fixing unit which
fixes the transferred toner image onto the transferred
material.
7. An image forming apparatus according to claim 6, further
comprising a printer controller which converts code data inputted
from an external apparatus into an image signal and inputs the
image signal to said light scanning apparatus.
8. A light scanning apparatus comprising: a semiconductor laser
which emits a light beam having a wavelength equal to or less than
450 nm; deflection means which uses the light beam, for scanning in
deflection, emitted from said light source means; an incidence
optical system which makes the light beam emitted from said
semiconductor laser incident on said deflection means; an imaging
optical system which images the light beam scanned in deflection by
said deflection means to a surface to be scanned; light splitting
means which splits part of the light beam emitted from said
semiconductor laser; light intensity detection means which detects
a light intensity of one flux of the light beam split by said light
splitting means; automatic power control means which automatically
controls a light emission output of said semiconductor laser on the
basis of a detection value detected by said light intensity
detection means; and a correction plate which is disposed between
said light splitting means and said light intensity detection
means, wherein said correction plate has an optical characteristic
that is the same as or proportional to fluctuations of spectral
transmittances of said incidence optical system and of said imaging
optical system, which are caused as a concomitant of a fluctuation
in wavelength of the light beam emitted from said semiconductor
laser.
9. An image forming apparatus comprising: a light scanning
apparatus according to claim 8; a photosensitive body which is
disposed on the scanned surface; a developing unit which develops,
as a toner image, an electrostatic latent image formed on said
photosensitive body by light beams used for scanning by said light
scanning apparatus; a transfer unit which transfers the developed
toner image onto a transferred material; and a fixing unit which
fixes the transferred toner image onto the transferred
material.
10. An image forming apparatus according to claim 9, further
comprising a printer controller which converts code data inputted
from an external apparatus into an image signal and inputs the
image signal to said light scanning apparatus.
11. A light scanning apparatus comprising: a semiconductor laser
which has a plurality of light emitting elements for emitting light
beams having a wavelength equal to or less than 450 nm; deflection
means which uses the light beams, for scanning in deflection,
emitted from said semiconductor laser; an incidence optical system
which directs the light beams emitted from said semiconductor laser
on said deflection means; an imaging optical system which images
the light beams scanned in deflection by said deflection means to a
surface to be scanned; and a wavelength fluctuation correction
plate which is disposed in a light path between said semiconductor
laser and said deflection means, wherein said wavelength
fluctuation correction plate is made from a material having a
spectral transmittance distribution for suppressing a difference in
the light intensity between light beams incident into said surface
to be scanned when there is a difference in the wavelength between
the light beams emitted from said semiconductor laser.
12. An image forming apparatus comprising: a light scanning
apparatus according to claim 11; a photosensitive body which is
disposed on the scanned surface; a developing unit which develops,
as a toner image, an electrostatic latent image formed on said
photosensitive body by light beams used for scanning by said light
scanning apparatus; a transfer unit which transfers the developed
toner image onto a transferred material; and a fixing unit which
fixes the transferred toner image onto the transferred
material.
13. An image forming apparatus according to claim 12, further
comprising a printer controller which converts code data inputted
from an external apparatus into an image signal and inputs the
image signal to said light scanning apparatus.
14. A light scanning apparatus comprising: a semiconductor laser
which emits a light beam having a wavelength equal to or less than
450 nm; an incidence optical system which makes the light beam,
emitted from said semiconductor laser, incident on a deflection
means for scanning in deflection; an imaging optical system which
images the light beam scanned in deflection by said deflection
means to a surface to be scanned; a temperature sensor which
detects a temperature of said semiconductor laser; prediction means
which predicts the fluctuations in the spectral transmittances of
said incidence optical system and of said imaging optical system,
which are caused as the concomitant of the fluctuation in the
wavelength of the light beams emitted from said semiconductor laser
on the basis of an output signal from said temperature sensor, and
outputs a prediction signal; and automatic power control means
which automatically controls the output of said light source means
on the basis of the prediction signal from said prediction
means.
15. An image forming apparatus comprising: said light scanning
apparatus according to claim 14; a photosensitive body which is
disposed on the scanned surface; a developing unit which develops,
as a toner image, an electrostatic latent image formed on said
photosensitive body by light beams used for scanning by said light
scanning apparatus; a transfer unit which transfers the developed
toner image onto a transferred material; and a fixing unit which
fixes the transferred toner image onto the transferred
material.
16. An image forming apparatus according to claim 15, further
comprising a printer controller which converts code data inputted
from an external apparatus into an image signal and inputs the
image signal to said light scanning apparatus.
17. A light scanning apparatus comprising: a semiconductor laser
which emits a light beam having a wavelength equal to or less than
450 nm; an incidence optical system which makes the light beam,
emitted from said semiconductor laser, incident on a deflection
means for performing scanning in deflection; an imaging optical
system which images the light beam scanned in deflection by said
deflection means to a surface to be scanned; light intensity
detection means which detects fluctuations in spectral
transmittances of said incidence optical system, which are caused
as a concomitant of a fluctuation in wavelength of the light beam
which is emitted from said semiconductor laser and passes through
said incident optical system; and automatic power control means
which automatically controls a light emission output of said
semiconductor laser on the basis of a detection value detected by
said light intensity detection means.
Description
This application claims the benefit of Japanese Patent Application
No. 2005-280432, filed Sep. 27, 2005, which is hereby incorporated
by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a light scanning apparatus and an
image forming apparatus using this light scanning apparatus, and is
suited to an image forming apparatus, such as a laser beam printer
and a digital copying machine that have an electrophotographic
process, and a multi-function printer.
2. Description of the Related Art
According to the prior art, in a light scanning apparatus, such as
a laser beam printer (LBP), light beams optically modulated and
emitted from a light source means are periodically deflected by a
light deflector (a polygon mirror, etc.) corresponding to image
signals. The deflected light beams are converged in a spot-like
shape on a photosensitive drum through a light scanning optical
system having a characteristic f.theta.. An image is recorded by
scanning with the converged light beam.
FIG. 16 is a principal schematic view of the conventional light
scanning apparatus.
Divergent light beams emitted from a light source means 81 are
substantially collimated by a collimator lens 83. The collimated
light beams are restricted by a stop 82 and are made to be incident
on a cylindrical lens 84. The cylindrical lens 84 has a
predetermined refracting power only in a subscanning direction. In
the collimated light beams incident on the cylindrical lens 84, the
light beams within a main scanning section emerge therefrom in an
as-is state. Further, within a subscanning section, the light beams
are converged and form an image substantially as a line image on a
deflection surface 85a of a deflection means 85 constructed of a
rotary polygon mirror.
Then, the light beams deflected by the deflection surface 85a of
the deflection means 85 are guided to a photosensitive drum surface
87 via an imaging optical system 86. Subsequently, the
photosensitive drum surface 87 is optically scanned in a direction
of an arrowhead B by rotating the deflection means 85 in a
direction of an arrowhead A.
In the light scanning apparatus described above, a BD sensor 89
defined as a photo detector is provided for adjusting timing of
starting the image formation on the photosensitive drum surface 87
before scanning the photosensitive drum surface 87 by the light
spots.
This BD sensor 89 receives BD light beams as part of the light
beams reflected in deflection by the light deflector 85. The BD
light beam connotes a light beam when scanning an area, excluding
an image formation area, before scanning the image formation area
on the photosensitive drum surface 87.
The BD light beam is reflected by a BD mirror 88 and becomes, after
being converged by a BD lens (not shown), incident upon the BD
sensor 89.
Then, a BD signal is detected from an output signal of the BD
sensor 89, and the detected BD signal is inputted to an image
processing unit 91. The inputted BD signal is taken in synchronism
with an image clock for scanning the image. Then, the timing of
starting of recording the image is controlled.
The image signal outputted from the image processing unit 91 is
outputted to a semiconductor laser operating unit 92 in accordance
with the image clock at an image write start timing. Further,
information given from photo-diodes disposed in the vicinity of the
laser within the semiconductor laser 81 is detected, and APC
(Automatic Power Control) is conducted, so that an emission power
of the semiconductor laser 81 becomes a standard light intensity
from this information.
An effect given by the APC is, however, to control the light
intensity from the semiconductor laser 81 to a predetermined value.
What is actually required, however, is to control the light
intensity on the photosensitive drum surface.
FIG. 17 shows a transmittance characteristic of a general type of
glass material. As shown in FIG. 17, generally, the transmittance
is substantially constant at 90% or larger up to the vicinity of a
visible wavelength of 450 nm from an infrared region. The glass,
however, generally absorbs the light in an ultraviolet region, and
hence, the wavelength of the transmissible light has a lower limit
(an absorption end). The transmittance abruptly decreases in a
region where the wavelength is shorter than a wavelength on the
order of 450 nm.
By the way, a much higher printing accuracy has been demanded of
the apparatus in recent years. There have recently been proposed a
variety of light scanning apparatus using a light source that
irradiates the light of which the wavelength is shorter than the
wavelength of 450 nm, such as a Blue laser (blue-violet
semiconductor laser) (see, for example, Japanese Patent Application
Laid-Open No. 2002-277803).
A contrivance of Japanese Patent Application Laid-Open No.
2002-277803 is that high color saturation of the print is attained
in a way that decreases a size of the light spot formed on the
scanned surface by the light scanning apparatus, which involves the
use of a light source irradiating the light, of which the
wavelength is equal to or shorter than the wavelength of 450
nm.
In the region of the wavelength equal to or less than 450 nm, as
described above, a change in the transmittance of the glass
material with respect to the change in the wavelength of the
semiconductor laser is larger in the conventional infrared
region.
Accordingly, when an oscillation wavelength of the laser changes
due to a change in temperature, even if the light intensity of the
semiconductor laser is kept constant by the APC operation, the
light intensity on the photosensitive drum surface does not become
constant, due to the change in the transmittance of each optical
element. As a result, such a problem arises that reproducibility of
the image cannot be preferably maintained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light
scanning apparatus capable of preventing a fluctuation in light
intensity on a photosensitive drum surface with respect to a
fluctuation in environment and a fluctuation in wavelength, keeping
preferable reproducibility of an image and satisfying an image
quality exhibiting high color saturation, and to provide an image
forming apparatus using this light scanning apparatus.
To accomplish the above object, an apparatus comprises control
means which controls an output of light source means on the basis
of a detection value detected by light intensity detection means,
wherein the control means controls an output of the light source
means when a temperature changes.
According to the present invention, it is possible to attain the
light scanning apparatus capable of preventing the fluctuation in
the light intensity on the photosensitive drum surface with respect
to the fluctuation in the environment and the fluctuation in the
wavelength, preferably keeping the reproducibility of the image and
obtaining the image quality exhibiting the high color saturation,
and to attain the image forming apparatus using this light scanning
apparatus.
Further features of the present invention will become apparent from
the following description of exemplary embodiments (with reference
to the attached drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a principal schematic view in a first Embodiment of the
present invention.
FIGS. 2A and 2B are principal sectional views in the first
Embodiment of the present invention.
FIG. 3 is a diagram showing a field curvature in the first
Embodiment of the present invention.
FIG. 4 is a flowchart of an APC control flow in the first
Embodiment of the present invention.
FIG. 5 is a principal schematic view in a second Embodiment of the
present invention.
FIG. 6 is a principal sectional view in the second Embodiment of
the present invention.
FIG. 7 is a graph showing the field curvature in the first
Embodiment of the present invention.
FIG. 8 is a graph showing a relationship between an Abbe number and
a change in transmittance in a short wavelength region of an
optical glass.
FIG. 9 is a graph showing a resin wavelength-transmittance
characteristic.
FIG. 10 is a principal schematic view in a third Embodiment of the
present invention.
FIG. 11 is a principal schematic view in the third Embodiment of
the present invention.
FIG. 12 is a principal schematic view in a fourth Embodiment of the
present invention.
FIG. 13 is an explanatory diagram showing how to perform correction
by use of a transmittance correction plate in a fourth Embodiment
of the present invention.
FIG. 14 is a view showing a subscanning section, illustrating an
Embodiment of an image forming apparatus of the present
invention.
FIG. 15 is a principal schematic view showing a color image forming
apparatus in an Embodiment of the present invention.
FIG. 16 is a principal schematic view of a conventional light
scanning apparatus.
FIG. 17 is a graphic chart showing a transmittance characteristic
of a glass material with respect to a wavelength.
DESCRIPTION OF THE EMBODIMENTS
Embodiments of the present invention will hereinafter be described
with reference to the drawings.
First Embodiment
FIG. 1 is a principal view (a principal perspective view) showing
an operational principle of a light scanning apparatus in a first
Embodiment of the present invention.
It should be noted that, in the following discussion, a main
scanning direction connotes a direction perpendicular to an axis of
rotation of a rotary polygon mirror and to an optical axis of an
imaging optical system. A subscanning direction represents a
direction parallel to the axis of rotation of the rotary polygon
mirror. Further, a main scanning section defines a plane covering
the main scanning direction and the optical axis of the imaging
optical system. Further, the subscanning section is a section
perpendicular to a main scanning section.
FIGS. 2A and 2B are principal sectional views each showing a
specific example of the first Embodiment of the present
invention.
FIG. 2A is the principal sectional view (the main scanning
sectional view) in the main scanning direction, and FIG. 2B is the
principal sectional view (the subscanning sectional view) in the
subscanning direction. FIG. 3 is a view depicting a field curvature
in the main scanning direction and in the subscanning direction in
the first Embodiment of the present invention.
In FIGS. 2A and 2B, reference numeral 1 represents a light source
means, which is, for instance, a blue-violet color semiconductor
laser oscillating light beams of which a wavelength .lamda. is
equal to or less than 450 nm (405 nm in the first Embodiment).
Reference numeral 3 designates a first lens (which is a cemented
lens of a negative lens 3a and a positive lens 3b) having a
positive refracting power (power). The first lens 3 performs a role
of collimating the light beams emitted from the semiconductor laser
1.
Reference numeral 7 denotes a second lens (a spherical lens) having
a negative refracting power. The second lens 7 performs a role of
converting the light beams collimated by the first lens 3 into
divergent light beams.
Reference numeral 2 stands for an aperture stop that reshapes a
shape of the light beams by restricting the passage of the light
beams. Reference numeral 4 represents an optical system (a
cylindrical lens) having a positive refracting power within the
subscanning section. The optical system 4 performs a role of
forming an image, substantially as a line image, the light beams
passing through the aperture stop 2 on a deflection surface 5a of a
light deflector 5, which will be explained later on, within the
subscanning section.
Reference numeral 9 represents a folding mirror (retro-reflection
mirror). The folding mirror 9 performs a role of folding a light
path of the light beams passing through the cylindrical lens 4
toward the optical deflector 5.
Note that the respective components such as the first lens 3, the
second lens 7, the aperture stop 2, the cylindrical lens 4, the
folding mirror 9, and first and second imaging lenses 6a, 6b, which
will be described later on, configure part of a first optical
system (incidence optical system) LA.
Moreover, an a focal system is built up by four pieces of lenses,
such as the second lens 7, the cylindrical lens 4, the first
imaging lens 6a and the second imaging lens 6b, which will
hereinafter be explained within the main scanning section.
Reference numeral 5 designates the optical deflector (the polygon
mirror) defined as a deflection means, and is rotated at a fixed
speed in a direction of an arrowhead A in FIG. 2 about an
axis-of-rotation 5a by a driving means (not shown), such as a
motor.
Reference numeral 6 stands for a second optical system (an imaging
optical system) having a characteristic f.theta., and includes the
first imaging lens 6a, the second imaging lens 6b and a third
imaging lens 6c. The first imaging lens 6a is a spherical lens
composed of a glass lens, and the second imaging lens 6b is a
cylindrical lens composed of a glass lens. The first and second
imaging lenses 6a, 6b perform a role of establishing compatibility
between the field curvature in the main scanning direction and the
characteristic f.theta..
The third imaging lens 6c is a plastic lens. The third imaging lens
6c is an anamorphic lens having powers different from each other in
the main scanning direction and in the subscanning direction. This
anamorphic lens satisfies the field curvature in the subscanning
direction.
Moreover, the first and second imaging lenses 6a, 6b also configure
part of the first optical system LA. Reference numeral 8 represents
a photosensitive drum surface serving as a surface to be
scanned.
Reference numeral 13 denotes a reflex mirror (which will
hereinafter be referred to as a (BD mirror)) disposed on a scanning
line in the main scanning direction. The BD mirror 13 performs a
role of reflecting the light beams (BD light beams) for synchronous
detection for adjusting timing of a scan start position on the
photosensitive drum surface 8, toward a synchronous detection
element 10.
Reference numeral 12 represents a slit (which will hereinafter be
termed a "BD slit") for the synchronous detection. The slit 12 is
disposed in a position equivalent to the photosensitive drum
surface 8 and determines an image write starting position.
Reference numeral 11 designates a condenser lens (which will
hereinafter be referred to as a "BD lens"). The BD lens 11 serves
to provide a conjugate relation between the BD mirror 13 and a BD
sensor 10 that will be explained later on. The condenser lens 11
compensates for surface-down of the BD mirror 13.
Reference numeral 10 stands for an optical sensor (which will also
hereinafter be referred to as a "BD sensor") serving as the
synchronous detection element. In the first Embodiment, the timing
of the scan start position for recording the image on the
photosensitive drum surface 8 is adjusted by use of a synchronous
signal (a BD signal) obtained by detecting an output signal from
the BD sensor 10.
It should be noted that the respective components, such as the BD
slit 12, the BD lens 11 and the BD sensor 10, configure part of a
write starting position detecting optical system (BD optical
system).
Reference numeral 14 represents a light intensity detection sensor
(photo detector) serving as a light intensity detection means. The
light intensity detection sensor 14 detects fluctuations in
spectral transmittances of the incidence optical system LA and of
the imaging optical system 6, which are caused as a concomitant of
a fluctuation in the wavelength of the light beams emitted from the
semiconductor laser 1.
The light intensity detection sensor 14 is disposed on the
photosensitive drum surface 8 or in a position conjugate to the
photosensitive drum surface 8 and disposed outside an effective
scanning area.
In the first Embodiment, when finishing writing the image on the
photosensitive drum surface 8 (or when starting the writing of the
image), a light intensity (a quantity of light) is measured as the
light beams travel through the light intensity detection sensor 14,
thereby detecting the fluctuations in the spectral transmittances
of the incidence optical system LA and of the imaging optical
system 6.
Reference numeral 15 designates a control means. The control means
15 controls (APC) the output of the semiconductor laser 1 to reach
a standard light intensity on the basis of a detection value
detected by the light intensity detection sensor 14. Reference
numeral 16 denotes a semiconductor laser operating unit. The
semiconductor laser operating unit 16 drives the semiconductor
laser 1 on the basis of a signal transmitted from the control means
15 or from an image processing unit 17 that will hereinafter be
described later on.
The image processing unit 17 detects the BD signal from the output
signal of the BD sensor 10, and takes synchronism with an image
clock for scanning the image. Then, the timing control for starting
recording of the image is conducted via the semiconductor laser
operating unit 16.
The light beams emitted in modulation from the semiconductor laser
1 are collimated by the first lens 3. Thereafter, the collimated
light beams are converted into the divergent light beams by the
second lens 7, and subsequently, the light beams are restricted by
the aperture stop 2 and are made incident on the cylindrical lens
4.
In the light beams incident upon the cylindrical lens 4, the light
beams within the subscanning section become, after being converged
and passing through the second imaging lens 6b and the first
imaging lens 6a, incident on a deflecting surface 5a of the light
deflector 5. An image of the light beams is formed as a
longitudinal line image in the main scanning direction in the
vicinity of the deflecting surface 5a.
At this time, the light beams incident on the deflecting surface 5a
are made incident at an oblique incident angle of 0.8 degree to the
plane perpendicular to the axis of rotation of the light deflector
5 from within the subscanning section including the axis of
rotation of the light deflector 5 and the optical axis of the
second optical system 6, thereby splitting the incident light beams
and the deflection light beams.
Note that the light source means 1 and the incidence optical system
LA shall exist within the main scanning section, for simplicity, in
FIG. 1.
Moreover, the light beams within the main scanning section become
divergent and pass through the second imaging lens 6b and the first
imaging lens 6a, and are, thereby, collimated. Thereafter, the
light beams are incident upon the center of an angle of deflection
of the light deflector 5 or upon the deflecting surface 5a
substantially from the center. At this time, a beam width of the
collimated light beams is set sufficiently large for a facet width
of the deflecting surface 5a of the light deflector 5 in the main
scanning direction. Then, the light beams reflected in deflection
by the deflecting surface 5a of the light deflector 5 are guided to
the photosensitive drum surface 8 via the first, second and third
imaging lenses 6a, 6b, 6c. The photosensitive drum surface 8 is
scanned by the light beams in a direction of an arrowhead B (in the
main scanning direction) by rotating the light deflector 5 in the
direction of the arrowhead A. With this scan, the image is recorded
on the photosensitive drum surface 8 defined as a recording
medium.
At this time, before scanning the photosensitive drum surface 8
with the light spots, the timing of starting of the image formation
on the photosensitive drum surface 8 is adjusted.
For attaining this, the BD sensor 10 receives the BD light beams as
part of the light beams reflected in deflection by the light
deflector 5. The BD light beams are reflected by the BD mirror 13,
and the light intensity thereof is restricted by the BD slit 12.
Then, the BD light beams are converged by the BD lens 11 and become
incident upon the BD sensor 10.
Then, the BD signal is detected from the output signal of the BD
sensor 10, and the timing of starting of recording of the image on
the photosensitive drum surface 8 is adjusted based on this BD
signal.
Table 1 shows an optical layout and shapes of the respective
lenses. Table 2 shows names of glass materials and Abbe numbers
thereof in the first Embodiment.
TABLE-US-00001 TABLE 1 wavelength in use .lamda. (nm) 405 scan
angle .theta. (deg) 50.41 coefficient f.theta. f 340.99 layout of
incidence system distance between light source and cemented lens d1
(mm) 33.04 central thickness of cemented lens (concave) d2 (mm)
2.04 central thickness of cemented lens (convex) d3 (mm) 3.00
distance between cemented lens and spherical lens d4 (mm) 10.02
central thickness of spherical lens d5 (mm) 5.00 distance spherical
lens and cylindrical lens d6 (mm) 19.04 central thickness of
cylindrical lens d7 (mm) 6.00 distance between cylindrical lens and
deflecting d8 (mm) 346.48 surface scan system layout distance
between deflecting surface and spherical D1 (mm) 19.87 lens central
thickness of spherical lens D2 (mm) 4 distance between spherical
lens and cylindrical D3 (mm) 41.5 lens central thickness of
cylindrical lens D4 (mm) 27.90 distance between cylindrical lens
and anamorphic D5 (mm) 228.41 lens central thickness of anamorphic
lens D6 (mm) 4.00 distance between anamorphic lens and scanned D7
(mm) 157.39 surface meridian line R sagittal line R first second
first second surface surface surface surface cemented lens
(concave) -17.58 -74.21 cemented lens (convex) 22.95 -17.58
spherical lens -56.34 .infin. -56.34 .infin. cylindrical lens
.infin. .infin. 48.15 .infin. shape of spherical lens shape of
cylindrical lens first second first second surface surface surface
surface R -338.563 .infin. .infin. -152.570 r -- -- .infin. .infin.
shape of anamorphic lens first surface second surface R -1000.000
-1000.000 r 141.115 -110.305
TABLE-US-00002 TABLE 2 Abbe number name of glass material (.nu.d)
cemented lens (concave) s-tih4 (OHARA) 27.51 cemented lens (convex)
s-bsm81 (OHARA) 60.07 spherical lens s-bs17 (OHARA) 64.14
cylindrical lens s-bs17 (OHARA) 64.14 spherical lens s-tih11
(OHARA) 25.68 cylindrical lens s-bah27 (OHARA) 41.24 anamorphic
lens E48R (ZEONEX) 55.50
In a commercially-available blue laser having a wavelength of 405
nm, when a temperature in the vicinity of the laser rises by twenty
degrees, the wavelength of the laser changes by 1 nm or more. At
this time, the fluctuations in the transmittances of the negative
lens 3a, the positive lens 3b, the spherical lens 7, the
cylindrical lens 4, the first imaging lens 6a, the second imaging
lens 6b and the third imaging lens 6c are sequentially given such
as 0.48%, 0.03%, 0.02%, 0.02%, 0.65%, 0.35%, 0.02%, respectively.
Moreover, the light beams from the semiconductor laser 1 pass
through twice each of the first and second imaging lenses 6a, 6b,
and hence, the fluctuation on the order of 2.55% occurs on the
photosensitive drum surface 8.
Generally, it is required that the fluctuation in the intensity of
light incident on the photosensitive drum surface 8 be within 0.5%
in order to satisfy reproducibility of a high image quality of a
photo, etc.
Such being the case, in the first Embodiment, the control, as shown
in a flowchart illustrated in FIG. 4, is conducted.
S101: Measurement of PD is started.
S102: An initial PD light intensity is measured.
S103: A judgment is made as to whether it is PD measurement timing
or not.
S104: When reaching the judgment timing, a present light intensity
is measured.
S105: The light intensity detection sensor 14 compares a detected
light intensity PD with an initial light intensity PD.sub.0.
S106: If there is no difference between PD and PD.sub.0, the
operation comes to an end.
S107: If there is the difference in the light intensity, the
control means 15 controls an applied current of the laser so as to
reach a predetermined light intensity on the photosensitive drum
surface 8.
Conducted in this way is the APC operation, taking account of the
fluctuation in the transmittance when traveling through the glass
material.
The procedures described above are repeated until the intensities
PD, PD.sub.0 are equalized, hereby restraining, within 0.5%, the
fluctuation in the light intensity on the photosensitive drum
surface 8. It is to be noted that the light intensity detection
sensor 14 and the BD sensor 10 are separately provided in the first
Embodiment, however, without being limited to this configuration,
such a configuration may be taken that, for example, the BD sensor
10 is provided with a means capable of detecting the light
intensity or the light intensity detection sensor 14 is provided
with a means capable of detecting the BD light beams. This
configuration enables the number of components to be reduced.
Second Embodiment
FIG. 5 is a principal view showing the principle of the light
scanning apparatus in a second Embodiment of the present invention.
FIG. 6 is a principal sectional view illustrating a specific
example of the second Embodiment of the present invention. FIG. 7
is a graph showing field curvatures in the main scanning direction
and in the subscanning direction in the second Embodiment of the
present invention. In FIGS. 5 and 6, the same components as those
depicted in FIGS. 1 and 2 are marked with the same numerals.
A different point of the second Embodiment from the first
Embodiment discussed above is that the light intensity detection
light beams deflected by the light deflector 5 are guided to the
light intensity detection sensor 14 without passing through the
imaging optical system 6. For example, the light intensity
detection sensor 14 is disposed between the light paths of the
light source means 1 and of the light deflector 5 (FIG. 6), or
disposed in a position for detecting the light beams between the
light paths of the light source means 1 and of the imaging optical
system 6 (FIG. 5). Other configurations and optical action are
substantially the same as those in the first Embodiment.
The detection of the light intensity involves the necessity for
irradiating the surface of the light intensity detection sensor 14
with the light beams for a fixed period of time. In the case of a
scanning optical system exhibiting a very high scanning speed over
the photosensitive drum surface 8, if the light intensity detection
sensor 14 for detecting the light intensity exists in the vicinity
of the photosensitive drum surface 8, there is a case in which the
light intensity cannot be precisely detected because of a short
period of time for which to pass through the light intensity
detection sensor 14.
Such being the case, in the second Embodiment, the light intensity
detection sensor 14 for detecting the fluctuation in the spectral
transmittance of the incidence optical system LA, which is caused
as the concomitant of the fluctuation in the wavelength of the
light beams emitted from the semiconductor laser 1, is disposed in
the position depicted in FIG. 5 or FIG. 6.
In FIG. 6, the light intensity detection sensor 14 is disposed in
the position for detecting the light beams between the light paths
of the semiconductor laser 1 and of the light deflector 5. In FIG.
5, the light intensity detection sensor 14 is disposed between the
light paths of the light source means 1 and of the imaging optical
system 6. With this configuration, the light intensity detecting
accuracy is improved.
In FIG. 6, the reflected light beams pass through the imaging
optical system 6 and travel toward the photosensitive drum surface
8 via a half mirror 20 provided between the cylindrical lens 4 and
the polygon mirror 5. On the other hand, the transmitted light
beams are, after passing through a stop 23, converged by a
spherical lens 22 and become incident on the light intensity
detection sensor 14, wherein the light intensity is measured.
In FIGS. 5 and 6, the light intensity detected by the light
intensity detection sensor 14 does not reflect the fluctuation in
the transmittance of the imaging optical system 6. This being the
case, in the second Embodiment, a material of the imaging optical
system 6 is properly selected.
In general, a transmittance T of the glass material can be
generally expressed as follows: T=exp(-4.pi.kd/.lamda.) (1) where d
is a thickness of the glass material, and k is called an extinction
coefficient.
An absorption end of the glass employed for the lens is required to
be set on the side of a short wavelength in order for the
short-wavelength light beams to penetrate the lens, and is small in
dispersion of the glass. Namely, the absorption end exists on the
shorter wavelength side, as a wavelength dependency of a refractive
index of the glass becomes smaller. It is desired that the
dispersion of the glass be small, in order to obtain high
transmittance also in the short wavelength light beams.
FIG. 8 shows an Abbe number v of a commercially available optical
glass and a fluctuation quantity of the transmittance when the
wavelength changes from 395 nm to 420 nm. The data in FIG. 8 are
obtained in a way that takes the glass manufactured by Ohara Corp.
for reference.
As is obvious from FIG. 8, there is less fluctuation in the
transmittance in the vicinity of the wavelength of 405 nm as the
Abbe number .nu. of the glass material becomes larger. Further, as
is apparent from the relational expression (1) given above, the
transmittance T becomes smaller, accordingly, as the glass material
becomes thicker.
Generally, the thickness of the lens configuring the incidence
optical system LA is on the order of 3 mm through 5 mm. As compared
with this, the thickness of the lens configuring the imaging
optical system 6 becomes comparatively as thick as 5 mm-10 mm, in
order to make preferable both of the characteristic f.theta. and
the quantity of the field curvature.
Therefore, a scatter in the light intensity on the photosensitive
drum surface 8 is not so improved, even when the light intensity is
kept constant by increasing the Abbe number of the glass material
that forms the imaging optical system 6, and by performing the APC
operation with the transmitted light intensity of only the
incidence optical system LA.
It is considered to be desirable from FIG. 8 that there is a small
fluctuation in the transmittance of the imaging optical system 6
due to the fluctuation in the wavelength, if the Abbe number of the
material of each of the imaging lenses configuring the imaging
optical system 6 is equal to or greater than forty.
Such being the case, in the second Embodiment, as shown in Table 4
given below, the glass materials each exhibiting an Abbe number
that is equal to or greater than forty are used for the first,
second and third imaging lenses 6a, 6b, 6c, serving as the
refraction optical elements building up the imaging optical system
6, thereby solving the problem described above.
Table 3 shows the optical layout and the shapes of the respective
lenses in the first Embodiment of the present invention. Table 4
shows the names of the glass materials of the respective lenses and
the Abbe numbers thereof in the second Embodiment.
TABLE-US-00003 TABLE 3 wavelength in use .lamda. (nm) 405 scan
angle .theta. (deg) 50.41 coefficient f.theta. f 337.43 layout of
incidence system distance between light source and cemented lens d1
(mm) 33.04 central thickness of cemented lens (concave) d2 (mm)
2.04 central thickness of cemented lens (convex) d3 (mm) 3.00
distance between cemented lens and spherical lens d4 (mm) 10.02
central thickness of spherical lens d5 (mm) 5.00 distance spherical
lens and cylindrical lens d6 (mm) 19.04 central thickness of
cylindrical lens d7 (mm) 6.00 distance between cylindrical lens and
deflecting d8 (mm) 346.48 surface scan system layout distance
between deflecting surface and spherical D1 (mm) 26.86 lens central
thickness of spherical lens D2 (mm) 14.15 distance between
spherical lens and toric lens D3 (mm) 50.08 central thickness of
toric lens D4 (mm) 21.74 distance between toric lens and anamorphic
lens D5 (mm) 163.57 central thickness of anamorphic lens D6 (mm)
7.50 distance between anamorphic lens and scanned D7 (mm) 165.39
surface meridian line R sagittal line R first second first second
surface surface surface surface cemented lens (concave) -17.58
-74.21 cemented lens (convex) 22.95 -17.58 spherical lens -56.34
.infin. -56.34 .infin. cylindrical lens .infin. .infin. 48.15
.infin. shape of spherical lens shape of cylindrical lens first
second first second surface surface surface surface R -89.588
-88.863 .infin. -226.618 r -- -- -159.940 shape of anamorphic lens
first surface second surface R -1126.436 -853.015 r .infin.
-93.762
TABLE-US-00004 TABLE 4 Abbe number name of glass material (.nu.d)
cemented lens (concave) s-tih4 (OHARA) 27.51 cemented lens (convex)
s-bsm81 (OHARA) 60.07 spherical lens s-bs17 (OHARA) 64.14
cylindrical lens s-bs17 (OHARA) 64.14 spherical lens s-bsm14
(OHARA) 60.64 toric lens s-bs17 (OHARA) 64.14 anamorphic lens E48R
(ZEONEX) 55.50
In the second Embodiment, as compared with the first Embodiment,
the fluctuation in the transmittance of the imaging optical system
6 is restrained down to 0.28%, even when the wavelength changes by
1 nm or greater in a way that changes the glass materials of the
first imaging lens 6a and of the second imaging lens 6b to s-bsm14
(Abbe number: 60.64) and to s-bsl7 (Abbe number: 64.14).
With this contrivance, there is a small fluctuation in the light
intensity on the photosensitive drum surface 8, even by performing
the APC control in a way that detects the light intensity after
passing through the imaging optical system 6.
Moreover, over the recent years, in many cases, a resinous lens
having an aspherical shape owing to injection molding has been used
for the imaging optical system 6, because it is easy to
manufacture, and for further improving the optical performance.
FIG. 9 shows the fluctuation in the transmittance with respect to
the wavelength of ZEONEX 480R (Abbe number: 56.2 (25.degree. C.,
d-line)) of which the thickness is 10 nm.
As is obvious from FIG. 9, the fluctuation in the spectral
transmittance is smaller than the glass, of which the Abbe number
is small, in a short-wavelength area. The resin exhibiting such a
wavelength characteristic is chosen for the imaging lens, thereby
making it possible to prevent any change of the light intensity on
the photosensitive drum surface 8.
Third Embodiment
FIG. 10 is a principal perspective view of the light scanning
apparatus in a third Embodiment of the present invention. In FIG.
10, the same components as those depicted in FIG. 1 are marked with
the same numerals.
A different point of the third Embodiment from the second
Embodiment is that the configuration for detecting the light
intensity is simplified. Therefore, the light intensity detection
sensor 14 is disposed in the vicinity of the semiconductor laser 1,
and a correction plate 19 is disposed anterior to the light
intensity detection sensor 14.
Other configurations and optical action are substantially the same
as those in the second Embodiment, whereby the same effects are
acquired.
In FIG. 10, reference numeral 18 represents a half mirror serving
as a beam splitting means. The half mirror 18 is provided in the
light path between the semiconductor laser 1 and the incidence
optical system LA. The half mirror 18 performs a role of splitting
the light beams emitted from the semiconductor laser 1 into two
fluxes of light, i.e., the transmitted light and the reflected
light, and directing the transmitted light toward the
photosensitive drum surface 8 and the reflected light toward the
light intensity detection sensor 14.
Reference numeral 19 designates the correction plate disposed in
the light path between the half mirror 18 and the light intensity
detection sensor 14. The correction plate 19 has an optical
characteristic that is substantially the same as or proportional to
the fluctuation in the spectral transmittance of each of the
incidence optical system LA and the imaging optical system 6, which
is caused as the concomitant of the fluctuation in the wavelength
of the light beams emitted from the semiconductor laser 1.
In the third Embodiment, in many cases, the first lens 3 involves
using a material having a high refractive index for making
preferable a wave front aberration of the collimated light beams to
be emitted. This type of glass material has an Abbe number that is
comparatively small, as low as forty or less.
Further, if a glass material capable of achromatizing with the
incidence optical system LA is selected in order to restrain a
fluctuation in focus on the photosensitive drum surface 8 due to
the fluctuation in the wavelength of the semiconductor laser 1, it
follows that a material combination is a combination of a material
exhibiting a large Abbe number and a material exhibiting a small
Abbe number.
Then, in the third Embodiment, the light intensity detection sensor
14 is disposed in the vicinity of the semiconductor laser 1, as
described above. Even in the case of conducting the APC operation,
the correction plate 19 having the above-mentioned optical
characteristic is disposed anterior to the light intensity
detection sensor 14 to enable prediction of a loss of the light
intensity in the incidence optical system LA. With this
arrangement, the same effect as that of the second Embodiment
discussed above, is obtained.
Herein, let I.sub.0(.lamda.) be an emission light intensity of the
semiconductor laser 1, and let T(.lamda.) be the transmittance of
the correction plate 19. An incidence light intensity I(.lamda.) to
the light intensity detection sensor 14 is given such as:
I(.lamda.)=T(.lamda.).times.I.sub.0(.lamda.). (2) Further,
supposing that the laser wavelength changes due to a change of an
ambient temperature, the incidence light intensity I(.lamda.)
becomes such as:
I(.lamda..sub.1)=T(.lamda..sub.1).times.I.sub.0(.lamda..sub.1). (3)
Herein, when performing the APC operation so that the incidence
light intensity I(.lamda.) to the light intensity detection sensor
14 is always constant without depending on .lamda., the following
formula is established.
I(.lamda.)=T(.lamda.).times.I.sub.0(.lamda.)=I(.lamda..sub.1)=T(.lamda..s-
ub.1).times.I.sub.0(.lamda..sub.1)
.thrfore.I.sub.0(.lamda..sub.1)={T(.lamda.)/T(.lamda..sub.1)}.times.I.sub-
.0(.lamda.). (4) The light intensity of the light incident on the
photosensitive drum surface 8 is corrected so as to correct the
spectral transmittance characteristic of the glass material.
The glass material and the thickness of the correction plate 19 are
selected so as to be substantially the same as or proportional to
the fluctuation in the transmittance of the whole system with
respect to the fluctuation in the wavelength. The correction plate
19 is disposed, whereby even when the wavelength of the
semiconductor laser 1 fluctuates, the light intensity on the
surface of the light intensity detection sensor 14 is substantially
equalized to the light intensity on the photosensitive drum surface
8. Hence, the light intensity on the photosensitive drum surface 8
can be substantially made constant by performing the APC operation.
Even if unable to obtain the glass material having the desired
spectral transmittance characteristic, a free design can be
attained by use of a dielectric multi-layered film, and hence, the
transmittance of the correction plate can be matched with the
spectral transmittance required.
It should be noted that the third Embodiment involves employing the
correction plate 19, however, for example, a detection sensitivity
of the light intensity detection sensor 14 may be set so as to be
substantially the same as or proportional to the fluctuation in the
transmittance of the whole system with respect to the fluctuation
in the wavelength.
Moreover, as depicted in FIG. 11, a temperature sensor 20 for
measuring in real-time a change of the temperature is disposed in
the vicinity of the semiconductor laser 1. Then, when a change of
the temperature is detected from an output signal transmitted from
the temperature sensor 20, a prediction means 21 predicts the
fluctuation in the spectral transmittance of each of the incidence
optical system LA and the imaging optical system 6, which is caused
as the concomitant of the fluctuation in the wavelength of the
light beams emitted from the semiconductor laser 1.
Then, the control means 15 controls the output of the semiconductor
laser 1 on the basis of the signal transmitted from the prediction
means 21. The configuration being thus made, the same effect as in
the third Embodiment discussed above is obtained.
Note that the third Embodiment has exemplified the APC operation
regarding the use of a single light source, however, the APC
operation is the same with respect to a plurality of light sources,
and is conducted in a way that lets the light beams through the
correction plate 19 for every light source, whereby a scatter in
density in each of the plural light sources is restrained.
Fourth Embodiment
FIG. 12 is a principal schematic view of the light scanning
apparatus in a fourth Embodiment of the present invention. The same
components as those depicted in FIG. 1 are marked with the same
numerals in FIG. 12.
A different point of the fourth Embodiment from the first
Embodiment discussed above is that a light source means 81 is
constructed of a vertical cavity surface emitting laser (VCSEL),
and a wavelength fluctuation correction plate 22 is provided in the
light path between the light source means 81 and the light
deflector 5. Other configurations and optical action are
substantially the same as those in the first Embodiment.
In FIG. 12, reference numeral 81 designates the light source means
having a plurality of light emitting points (light emitting
elements). For instance, the light source means 81 is constructed
of the vertical cavity surface emitting laser of such a type that
the wavelength of the plurality of light beams is equal to or less
than 450 nm.
Reference numeral 22 represents the wavelength fluctuation
correction plate. The wavelength fluctuation correction plate 22 is
made from a material having a spectral transmittance distribution
reversed to the spectral transmittance distributions of the
incidence optical system LA and of the imaging optical system 6 in
a fluctuation area of the wavelength of the light beams emitted
from the light source means 81.
Moreover, the wavelength fluctuation correction plate 22 has a
spectral transmittance distribution that reduces a difference in
light intensity between the light beams when the respective light
beams become incident on the scanned surface, even when there is a
difference in wavelength between the light beams emitted from the
plurality of light emitting elements of the light source means
81.
In the fourth Embodiment, the plurality of divergent light beams
emitted from the vertical cavity surface emitting laser 81 are
converted into convergent light beams by the first lens 3.
Thereafter, the light beams are reshaped into a desired beam shape
by the aperture stop 2 and then become incident upon the
cylindrical lens 4. The intra-main-scanning-section light beams
incident upon the cylindrical lens 4 emerge from the cylindrical
lens 4 in an as-is state. Further, within the subscanning section,
the light beams are converged and then imaged substantially as a
line image on the deflecting surface 5a of the light deflector
5.
Then, the plurality of light beams reflected in deflection by the
deflecting surface 5a of the light deflector 5 are imaged in spot
shapes on the photosensitive drum surface 8 by the imaging optical
system 6.
The photosensitive drum surface 8 is scanned by the plurality of
light beams at an equal speed in the direction of the arrowhead B
in a way that rotates the light deflector 5 in the direction of the
arrowhead A. Thus, the photosensitive drum surface 8 is scanned
simultaneously by the plurality of scanning lines, thereby
recording the image.
At this time, the BD sensor 10 is provided for adjusting the timing
of starting at the image formation, before scanning the
photosensitive drum surface 8 with the light spots. The BD sensor
10 receives the BD light beams defined as part of the light beams
reflected in deflection by the light deflector 5, i.e., the light
beams when scanning the area excluding the image forming area
before scanning the image formation area on the photosensitive drum
surface 8. The BD light beams are reflected by the BD mirror 13,
then converged by the BD lens (not shown) and are incident upon the
BD sensor 10. Then, the BD signal (the synchronous signal) is
detected from the output signal of this BD sensor 10, and the image
recording start timing on the photosensitive drum surface 8 is
adjusted based on this BD signal.
Herein, since there might be a possibility of expending a
tremendous length of time if the APC operation is conducted by
individually detecting the light intensity while causing each of
the plurality of light emitting elements to emit the light,
generally, the light intensity is detected by picking up one or
several light emitting elements.
If each individual light emitting element of the vertical cavity
surface emitting laser has a scatter in wavelength, however, it
follows that the light intensity on the photosensitive drum surface
8 differs at each light emitting element, due to a difference in
the transmittance of the glass material with respect to the
wavelength.
Such being the case, the fourth Embodiment solves the
above-mentioned problem by providing, as depicted in FIG. 12, the
wavelength fluctuation correction plate 22 in the light path
between the cylindrical lens 4 and the light deflector 5. The
wavelength fluctuation correction plate 22 is made from a material
having a spectral transmittance distribution reversed to the
spectral transmittance distributions of the incidence optical
system LA, and of the imaging optical system 6, in the fluctuation
area of the wavelength of the light beams emitted from the vertical
cavity surface emitting laser 81.
Besides, the wavelength fluctuation correction plate 22 has the
spectral transmittance distribution that reduces the difference in
light intensity between the light beams when the respective light
beams become incident on the scanned surface even if there is a
difference in wavelength between the light beams emitted from the
plurality of light emitting elements of the vertical cavity surface
emitting laser 81.
FIG. 13 shows a transmittance characteristic of the wavelength
fluctuation correction plate 22. Further, Table 5 shows a film
material and a film thickness of the dielectric multi-layered film
in the wavelength fluctuation correction plate 22 in the fourth
Embodiment.
TABLE-US-00005 TABLE 5 film material film thickness (nm) base
material s-bs17 (OHARA) -- first layer ZrO.sub.2 150 second layer
MgF.sub.2 200
A spectral transmittance distribution T'(.lamda.) of the wavelength
fluctuation correction plate 22 has, when letting A(.lamda.) be a
spectral transmittance distribution after passing through all the
glass materials, the following characteristic as indicated by a
bold solid line in a wavelength scatter range (which is an area
encompassed by a frame in the Figure) of the respective light
emitting elements: T'(.lamda.)=const./A(.lamda.). (5) Accordingly,
even when there is the scatter in the wavelength of the vertical
cavity surface emitting laser 81, the light intensity on the
photosensitive drum surface 8 can be made substantially constant by
the transmission through the wavelength fluctuation correction
plate 22. It is feasible to match with the spectral transmittance
that can meet the relational expression (5), because of attaining
the free design owing to the dielectric multi-layered film.
The fourth Embodiment has exemplified the vertical cavity surface
emitting laser. Without being limited to this vertical cavity
surface emitting laser, however, the spectral transmittance
characteristic of the wavelength fluctuation correction plate 22
may be determined corresponding to the scatter in the wavelength
also with respect to a system configured by, e.g., a plurality of
light sources (lasers).
(Image Forming Apparatus)
FIG. 14 is a principal sectional view taken in the subscanning
direction, showing an Embodiment of an image forming apparatus
according to the present invention. In FIG. 14, reference numeral
104 represents the image forming apparatus. Code data Dc is
inputted to this image forming apparatus 104 from an external
apparatus 117, such as a personal computer. The code data Dc is
converted into image data (dot data) Di by a printer controller 111
within the apparatus. This image data Di is inputted to a light
scanning unit 100 having a configuration illustrated in any one of
the first through fourth Embodiments. Then, a light beam 103, which
is modulated corresponding to the image data Di, is emitted from
this light scanning unit 100, and a photosensitive surface of a
photosensitive drum 101 is scanned by this light beam 103 in the
main scanning direction.
The photosensitive drum 101, defined as an electrostatic latent
image bearing body (photosensitive body), is rotated clockwise by a
motor 115. Then, with this rotation, the photosensitive surface of
the photosensitive drum 101 moves in the subscanning direction
orthogonal to the main scanning direction with respect to the light
beam 103. A charging roller 102, which uniformly charges the
surface of the photosensitive drum 101 with electricity, is so
provided as to abut the surface thereof. Then, the surface of the
photosensitive drum 101, charged by the charging roller 102, is
irradiated with the light beam 103 used for scanning by the light
scanning unit 100.
As explained earlier, the light beam 103 is modulated based on the
image data Di. An electrostatic latent image is formed on the
surface of the photosensitive drum 101 by irradiating this surface
with the light beam 103. This electrostatic latent image is
developed into a toner image by a developing unit 107 disposed so
as to abut the photosensitive drum 101, on a more downstream side
in the rotating direction of the photosensitive drum 101, than the
irradiating position of the light beam 103.
The toner image developed by the developing unit 107 is transferred
onto a sheet 112 defined as a transferred material by a transfer
roller 108 disposed downwardly of the photosensitive drum 101 in a
face-to-face relationship with the photosensitive drum 101.
Normally, the sheets 112 are stored in a sheet cassette 109
provided in front (on the right side in FIG. 14) of the
photosensitive drum 101. The sheets 112 can be fed manually. A
sheet feed roller 110 is provided at an edge portion of the sheet
cassette 109 and conveys the sheets 112 within the sheet cassette
109 to a conveyance path.
The sheet 112 undergoing the transfer of the not-yet-fixed toner
image in the manner described above is further conveyed to a fixing
unit provided in the rear (on the left side in FIG. 14) of the
photosensitive drum 101. The fixing unit is constructed of a fixing
roller 113 including a fixing heater (not shown), provided inside,
and a pressurizing roller 114 disposed so as to be press-fitted to
the fixing roller 113.
The sheet 112 conveyed from the transfer unit is heated while being
pressurized at a press-contact portion between the fixing roller
113 and the pressurizing roller 114, thereby fixing the
not-yet-fixed toner image onto the sheet 112. Further, a sheet
discharge roller 116 is disposed posterior to the fixing roller 113
and discharges the image-fixed sheet 112 outside the image forming
apparatus.
The printer controller 111, though not illustrated in FIG. 14,
controls the respective components represented by the motor 115
within the image forming apparatus and the polygon motor within the
light scanning unit, which will be described later, as well as
converting the data explained earlier.
A recording density of the image forming apparatus employed in the
present invention is not particularly limited. Considering that a
higher image quality is requested of the apparatus as the recording
density becomes higher, however, the first through fourth
Embodiments of the present invention exhibit more of the effects in
the image forming apparatus that is equal to or greater than 1200
dpi in recording density.
(Color Image Forming Apparatus)
FIG. 15 is a principal schematic view of a color image forming
apparatus in an Embodiment of the present invention. The present
Embodiment exemplifies a tandem type of color image forming
apparatus, wherein four pieces of light scanning apparatuses are
arranged in a side-by-side relationship and record the image
information in parallel on the photosensitive drum surface defined
as an image bearing body.
In FIG. 15, reference numeral 60 designates the color image forming
apparatus, and reference numerals 61, 62, 63, 64 represent the
light scanning apparatuses having any one of the configurations
shown in the first through fourth Embodiments.
Reference numerals 21, 22, 23, 24 denote the photosensitive drums
each defined as the image bearing body, reference numerals 31, 32,
33, 34 stand for developing unit, and reference numeral 51
represents a conveyance belt.
In FIG. 15, respective color signals of R (red), G (green) and B
(blue) are inputted to the color image forming apparatus 60 from an
external apparatus 52, such as a personal computer. These color
signals are converted by the intra-apparatus printer controller 53
into image data (dot data) of C (cyan), M (magenta), Y (yellow) and
B (black). The image data are inputted to the light scanning
apparatuses 61, 62, 63, 64, respectively. Then, light beams 41, 42,
43, 44, modulated corresponding to the image data, are emitted from
these light scanning apparatuses, and scan the photosensitive
surfaces of the photosensitive drums 21, 22, 23, 24 in the main
scanning direction.
In the color image forming apparatus in the present Embodiment, the
four light scanning apparatuses (61, 62, 63, 64) are arranged
corresponding to C (cyan), M (magenta), Y (yellow) and B (black).
The respective light scanning apparatuses record the image signals
(image information) on the surfaces of the photosensitive drums 21,
22, 23, 24.
In the color image forming apparatus in the present Embodiment, as
described above, the four light scanning apparatuses 61, 62, 63, 64
form the respective latent color images on the surfaces of the
photosensitive drums 21, 22, 23, 24 corresponding thereto by use of
the light beams based on the image data.
Thereafter, the images are multiplex-transferred onto the recording
material, thereby forming a single sheet of full-color image.
The external apparatus 52 may involve using, for example, a color
image reading apparatus including a CCD sensor. In this case, a
color digital copying machine is constructed of this color image
reading apparatus and the color image forming apparatus 60.
As many apparently widely different embodiments of the present
invention can be made without departing from the sprit and scope
thereof, it is to be understood that the invention is not limited
to the specific embodiments thereof except as defined in the
appended claims.
While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed exemplary embodiments. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
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